Mems electrometer that measures amount of repulsion of adjacent beams from each other for static field detection

ABSTRACT

An apparatus for detecting a static field includes a microelectromechanical systems (MEMS) device having two cantilevered beams of conductive material that are adjacent and substantially parallel to each other. The two beams repel each other in the presence of a static field. At least one sensor detects a respective amount of displacement of the two cantilevered beams from a rest position and determines an amount of repulsion of the two cantilevered beams from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following copending U.S.applications:

1. U.S. application Ser. No. 12/______ filed ______ entitled “Foil LeafElectrometer for Static Field Detection with Permanently SeparatingLeaves.”

2. U.S. application Ser. No. 12/______ filed ______ entitled “Foil-LeafElectrometer for Static Field Detection with Triggered Indicator.”

BACKGROUND OF THE INVENTION

Electronics, such as those found on printed circuit boards (PCBs), canbe very sensitive, and are likely to be damaged in the presence of aelectrostatic (static) field. Such fields can be encountered duringmanufacturing, handling, shipping, and use of PCBs. Even the failure ofa component as simple as a transistor on a PCB can be enough to ruin alarger device, such as a computer. The Electrostatic Discharge (ESD)Association has even proliferated Specification S20.20, which requiresthat all charge-generating materials that have electrostatic fields thatexceed 2,000 volts (V) should be kept at least twelve inches away fromESD sensitive products at all times. Industrial sheet plastic webpackaging and fluid cleaning processes are just a few of the many otherapplications that are also capable of generating damaging electrostaticfields.

A simple method of detecting the presence of an electric field wasdeveloped in the late 1700's. Two thin gold leaves are suspended from aconductive rod, forming a “gold-leaf electrometer.” By contacting theconductive rod with an electrified piece of material, the gold leavesbecome identically charged through induction and repulse one another.This device is regarded as inaccurate and unstable.

Modern electrometers employ more sophisticated and accurate techniquesof detecting and measuring the presence of charge. However, thesedevices can be expensive and are impractical for detecting fields undercertain circumstances, such as within small equipment or fluids.

BRIEF SUMMARY OF THE INVENTION

An apparatus is provided for detecting a static field includes amicroelectromechanical systems (MEMS) device having two cantileveredbeams of conductive material that are adjacent and substantiallyparallel to each other. The two beams repel each other in the presenceof a static field. At least one sensor detects a respective amount ofdisplacement of the two cantilevered beams from a rest position anddetermines an amount of repulsion of the two cantilevered beams fromeach other.

An apparatus is also provided for detecting a static field includes aMEMS device having two frangible cantilevered beams of conductivematerial that are adjacent and substantially parallel to each other. Thetwo frangible cantilevered beams repel each other in the presence of astatic field. At least one of the two frangible cantilevered beamsfractures upon a repulsion of the two beams from each other by at leasta predetermined distance.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustration, there is shown in the drawings an embodiment which ispresently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is an enlarged perspective view of two surfaces for detecting thepresence of a static field that may be used in preferred embodiments ofthe present invention as shown in FIGS. 4-15;

FIG. 2 is an enlarged perspective view of two surfaces adjacent to eachother in a rest position that may be used in preferred embodiments ofthe present invention as shown in FIGS. 4-15;

FIG. 3 is an enlarged perspective view of one of the surfaces of FIGS. 1or 2;

FIG. 4 is an enlarged perspective view of a static detecting apparatushaving a rupturable indicator filled with encapsulated material inaccordance with a preferred embodiment of the present invention;

FIG. 5 is an enlarged perspective view of the static detecting apparatusof FIG. 4 following a rupturing of the indicator;

FIG. 6 is an enlarged perspective view of a static detecting apparatushaving a rupturable adhesive indicator in accordance with anotherpreferred embodiment of the present invention;

FIG. 7 is an enlarged perspective view of a static detecting apparatushaving a rupturable dimple weld indicator in accordance with anotherpreferred embodiment of the present invention;

FIG. 8 is a schematic view of a static detecting apparatus having abistable multivibrator electrical circuit and an indicator in accordancewith another preferred embodiment of the present invention;

FIG. 9 is a schematic view of a static detecting apparatus having anoptical sensor and an indicator in accordance with another preferredembodiment of the present invention;

FIG. 10 is an enlarged perspective view of a static detecting apparatuswherein the surfaces exhibit a permanent bending in accordance withanother preferred embodiment of the present invention;

FIG. 11 is an enlarged perspective view of a static detecting apparatuswherein the surfaces have fractured in accordance with another preferredembodiment of the present invention;

FIG. 12 is an enlarged side elevational view of a static detectingapparatus having stoppers in accordance with another preferredembodiment of the present invention;

FIG. 13 is an enlarged side elevational view of a static detectingapparatus having a plurality of incrementally spaced apart stoppers inaccordance with another preferred embodiment of the present invention;

FIG. 14 is a schematic view of a static detecting apparatus havingstoppers coupled to an electric circuit and an indicator in accordancewith another preferred embodiment of the present invention;

FIG. 15 is an enlarged side elevational view of a static detectingapparatus wherein one of the surfaces is fixed in accordance withanother preferred embodiment of the present invention;

FIG. 16 is a schematic view of a static detecting apparatus having aMEMS device with two cantilevered beams in accordance with anotherpreferred embodiment of the present invention;

FIG. 17 is an enlarged perspective view of the static detectingapparatus of FIG. 16 wherein the cantilevered beams are adjacent andsubstantially parallel to one another in a rest position;

FIG. 18 is a schematic view of the static detecting apparatus of FIG. 16wherein the cantilevered beams are fractured;

FIG. 19 is an enlarged perspective view of a printed circuit boardhaving a static detecting apparatus mounted thereto in accordance withpreferred embodiments of the present invention;

FIG. 20 is an enlarged perspective view of a static shield bag having astatic detecting apparatus mounted thereto in accordance with preferredembodiments of the present invention;

FIG. 21 is an enlarged partial perspective view of an integrated circuitshipping tube having a static detecting apparatus mounted thereto inaccordance with preferred embodiments of the present invention;

FIG. 22 is a schematic view of a container of liquid having a staticdetecting apparatus disposed therein in accordance with preferredembodiments of the present invention; and

FIG. 23 is a schematic view of an ionizing system having a staticdetecting apparatus mounted thereto in accordance with preferredembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower”, and“upper” designate directions in the drawings to which reference is made.The words “inwardly” and “outwardly” refer to directions toward and awayfrom, respectively, the geometric center of the apparatus and designatedparts thereof. The terminology includes the above-listed words,derivatives thereof, and words of similar import. Additionally, thewords “a” and “an”, as used in the claims and in the correspondingportions of the specification, mean “at least one.” In the drawings, thesame reference numerals indicate like elements throughout.

FIG. 1 shows two surfaces 10 a, 10 b of a conductive material for use inpreferred embodiments of the present invention. The conductive materialmay be copper, silver, aluminum, tin, gold, or another conductive metal,conductive plastic, a doped semiconductive material (e.g., silicon), orcombinations thereof. The surfaces 10 a, 10 b may be respective surfacesof two beams 12 a, 12 b, but may also be fastened to, adhered to, orcoated onto the beams 12 a, 12 b. The beams 12 a, 12 b may beconstructed of a conductive material (either similar to or differentfrom the material of the surfaces 10 a, 10 b), an insulative material,or a semiconductive material. The beams 12 a, 12 b and the surfaces 10a, 10 b are preferably fastened at a common end 14.

The beams 12 a, 12 b and/or the surfaces 10 a, 10 b may be formed by asingle folded piece of conductive material, but may also be separate anddistinct bodies that are fastened together or in close proximity to oneanother at the common end 14 (see FIG. 2). In preferred embodiments, thesurfaces 10 a, 10 b face each other. As shown in FIG. 3, the surface 10a has a length dimension L and a width dimension W. The surface 10 aalso has a thickness dimension T, which is illustrated in FIG. 3 asbeing the thickness T of the entire beam 12 a for instances when thesurface 10 a is a surface of the beam 12 a of the same conductivematerial. When the surface 10 a is fastened or adhered to the beam 12 a,the thickness T includes only a thickness of the surface 10 a. Surface10 b preferably is identically sized with respect to surface 10 a. Inpreferred embodiments, the ratio of length L to width W to thickness Tis 1 unit by 0.25 units by 0.001 units. For example, surfaces 10 a, 10 bof tin with dimensions of 1 inch by 0.25 inches by 0.001 inches exhibitsa 2 inch separation in a 20 kilo-Volt (kV) static field, illustrated byfield lines 16 in FIG. 1.

The surfaces 10 a, 10 b are preferably electrically coupled to eachother, which is achieved in FIG. 1 by direct contact of the two surfaces10 a, 10 b near the common end 14, although other techniques forelectrical coupling may be utilized, such as by connecting the twosurfaces 10 a, 10 b via a conductive material at the common end 14. As aresult, the two surfaces 10 a, 10 b will be charged by field inductionin the presence of a static field 16. Prior to being subjected to astatic field 16, the two surfaces 10 a, 10 b are preferably adjacent toeach other (see, e.g., FIG. 2), and may be substantially parallel toeach other.

FIG. 4 illustrates an apparatus 100 for detecting a static field 16 inaccordance with certain preferred embodiments of the present invention.The apparatus 100 contains the two surfaces 10 a, 10 b and a rupturableindicator 122 that bridges and couples the surfaces 10 a, 10 b. Theindicator 122 ruptures (e.g., FIG. 5) upon repulsion of the two surfaces10 a, 10 b by at least a predetermined distance. The predetermineddistance may, for example, be calculated to correspond to a thresholdstatic field 16 strength that is undesirable for the particularapplication. The two surfaces 10 a, 10 b and the indicator 122 arepreferably surrounded by a clear insulative cover 28, which may beformed from glass, plastic, or the like and can be used for applicationsrequiring complete enclosure, such as during fluid immersions, withoutaffecting the performance of the apparatus 100.

The indicator 122, shown in FIG. 4 as a capsule, may include anencapsulated material 124 that is releasable from the indicator 122 uponrupture. The capsule 122 may be made from a thin, fragile plastic orother suitable material. The capsule 122 is preferably coupled to thesurfaces 10 a, 10 b using a strong adhesive (not shown), or may bewelded to the surfaces 10 a, 10 b. The encapsulated material 124 ispreferably a dye, but may also be an ink, gel, powder, or the like. Theapparatus 100 also preferably includes a surrounding medium 126 thatreceives the encapsulated material 124 released by the rupturedindicator 122. The surrounding medium 126 preferably undergoes a visiblecolor change upon receipt of the encapsulated material 124. For example,the surrounding medium 126 may be a blotting paper or fabric thatabsorbs the released dye 124, as shown in FIG. 5. The visible colorchange in FIG. 5 is most concentrated at the center, but more diffuse atedge regions of the apparatus 100, although over time the visible colorchange of the surrounding medium 126 may become more uniform. Thesurrounding medium 126 may also be a liquid that undergoes a visiblecolor change as the encapsulated material 124 becomes mixed with theliquid. Alternatively, the surrounding medium 126 may be air or anothergas that does not visibly change color. In certain embodiments, theencapsulated material 124 may visibly change color upon exposure to thesurrounding medium 126.

In an alternate embodiment, shown in FIG. 6, the rupturable indicator222 of the apparatus 200 is a bead of adhesive which may break apart orseparate from one or both of the surfaces 10 a, 10 b upon repulsion ofthe surfaces 10 a, 10 b by a predetermined distance. The adhesive bead222 is preferably visually inspected for damage following use, such asunder a microscope or by direct observation. In a further alternateembodiment, shown in FIG. 7, the rupturable indicator 322 of theapparatus 300 may be a dimple weld including, for example, a concavity329 a and a protrusion 329 b. The protrusion 329 b is initially disposedwithin the concavity 329 a, but repulsion of the surfaces 10 a, 10 b bya predetermined distance separates the protrusion 329 b from theconcavity 329 a, as shown in FIG. 7. The fit between the concavity 329 aand the protrusion 329 b is constructed such that the protrusion 329 bcannot reenter the concavity 329 a upon a return of the surfaces 10 a,10 b to the initial adjacent position.

FIG. 8 illustrates an apparatus 400 for detecting a static field 16 inaccordance with certain other preferred embodiments of the presentinvention. The apparatus 400 includes a sensor 432 that detectsrepulsion of the two surfaces 10 a, 10 b from each other by at least apredetermined distance. The apparatus 400 further includes an indicator434 coupled to an output of the sensor 432. The indicator 434communicates that repulsion of the two surfaces 10 a, 10 b has exceededthe predetermined distance.

In FIG. 8, the sensor 432 is illustrated as a conventional bistablemultivibrator electrical circuit and the indicator 434 is a light. Otherindicators 434 may also be used, such as, for example, audible alarms,electrical signals, or wireless signals. Preferably, the light 434 isinitially off, but may also initially be on. Once the two surfaces 10 a,10 b repulse one another by a predetermined distance, the bistablemultivibrator electrical circuit 432 changes states, which thereaftertriggers a change in the light 434. The light 434, which preferably wasinitially off, turns on. With the light 434 on, a user is now aware thatthe apparatus 400 was subjected to at least a threshold level of astatic field 16.

The bistable multivibrator electrical circuit 432 preferably includes atleast one trigger 436 for actuation by one or more of the surfaces 10 a,10 b or beams 12 a, 12 b. For example, the apparatus 400 may include twotriggers 436 that are contact pads set apart at the predetermineddistance. Repulsion of the surfaces 10 a, 10 b may then cause the beams12 a, 12 b to touch the contact pads 436 to conduct electricity to thebistable multivibrator electrical circuit 432. The trigger 436 may alsobe a mechanical switch, a capacitor, or the like. Preferably, subsequentrepulsion of the two surfaces 10 a, 10 b by a predetermined distancedoes not change the state of the sensor 432 or the indicator 434.

Similar to the embodiments shown in FIGS. 4-7, the surfaces 10 a, 10 b,the sensor 432, and the indicator 434 may all be contained within aclear insulative cover 28, but it is also envisioned that individualcomponents, particularly the indicator 434, may be external or separateand apart from at least the surfaces 10 a, 10 b.

In an alternate embodiment, shown in FIG. 9, sensor 532 of apparatus 500is an optical sensor. For example, a light source 538 may be opticallycoupled with the sensor 532. The light source 538 may initially beblocked by the surfaces 10 a, 10 b and/or beams 12 a, 12 b, and uponrepulsion of the surfaces 10 a, 10 b from each other by a predetermineddistance, the light source 538 is exposed to the sensor 532, triggeringan indicator 534, which may be a light. Alternatively, during repulsionby the surfaces 10 a, 10 b by a predetermined distance, one of thesurfaces 10 a, 10 b and/or beams 12 a, 12 b may block the light source538 from the sensor 532, triggering the indicator 534. As before,subsequent repulsion of the two surfaces 10 a, 10 b by a predetermineddistance preferably does not change the state of the sensor 532 or theindicator 534.

FIG. 10 illustrates an apparatus 600 for detecting a static field 16 inaccordance with another preferred embodiment of the present invention.The surfaces 10 a, 10 b and/or beams 12 a, 12 b have a deformationproperty such that stress caused by repulsion of the two surfaces 10 a,10 b from each other by at least a predetermined distance causes atleast one of the surfaces 10 a, 10 b and/or beams 12 a, 12 b topermanently deform. That is, the surfaces 10 a, 10 b do not completelyreturn to be adjacent to one another as the surfaces 10 a, 10 b had beenprior to exposure to the static field 16, as shown in FIG. 2. Forexample, the conductive material may have a degree of plasticity suchthat the stress caused by repulsion of the two surfaces 10, 10 b fromeach other by at least a predetermined distance causes at least one ofthe surfaces 10 a, 10 b to bend permanently. In FIG. 10, ends of thesurfaces 10 a, 10 b opposite to the common end 14 exhibit outward curldeformations 642 a, 642 b. The curls 642 a, 642 b provide a visualindication that the surfaces 10 a, 10 b have experienced at least athreshold level of a static field 16. At the dimensions of 1 inch by0.25 inches by 0.001 inches described above, surfaces 10 a, 10 b made ofaluminum exhibit clearly visible curl deformations 642 a, 642 b, unliketin surfaces 10 a, 10 b having identical dimensions.

In an alternate embodiment, shown in FIG. 11, the surfaces 10 a, 10 band/or beams 12 a, 12 b of apparatus 700 include a conductive materialhaving a fracture point such that the stress caused by repulsion of thetwo surfaces 10, 10 b from each other by at least a predetermineddistance causes at least one of the surfaces 10 a, 10 b to fracture. InFIG. 11, ends of the surfaces 10 a, 10 b opposite to the common end 14are broken off, leaving fractured ends 744 a, 744 b, indicating that thesurfaces 10 a, 10 b have experienced at least a threshold level of astatic field 16. For example, the beams 12 a, 12 b may be constructedfrom an extremely brittle material, such as thin quartz or glass, havinga conductive coating forming the conductive surfaces 10 a, 10 b.

Detection of the deformation of the surfaces 10 a, 10 b preferablyoccurs by visual inspection, either directly or using magnification.However, other methods may be used, such as optical sensors orelectrical sensors.

FIG. 12 illustrates an apparatus 800 for detecting a static field 16 inaccordance with another preferred embodiment of the present invention.In previous embodiments, at least one of the surfaces 10 a, 10 b has amovement path resulting from the repulsion of the two surfaces 10 a, 10b from each other. That is, the surfaces 10 a, 10 b tend to move awayfrom the rest position (e.g., FIG. 2) when in the presence of a staticfield 16. The apparatus 800 includes at least one stopper 852 a in themovement path of at least one of the surfaces 10 a. Preferably, astopper 852 a, 852 b is located in each respective movement path of thetwo surfaces 10 a, 10 b. The stoppers 852 a are “one-way stoppers” andprevent the respective surfaces 10 a, 10 b from returning to the restposition after the two surfaces 10 a, 10 b are repulsed from each otherby at least a predetermined distance.

In preferred embodiments, the stoppers 852 a, 852 b may be protrusionsplaced at the predetermined distance. The stoppers 852 a, 852 b shouldtherefore be shaped to allow the surfaces 10 a, 10 b to traverse thestoppers 852 a, 852 b during repulsion, but prevent the surfaces 10 a,10 b from traversing back to the rest position. For example, thesurfaces 10 a, 10 b and beams 12 a, 12 b are shown in phantom in FIG. 12when bending to traverse the respective stoppers 852 a, 852 b duringrepulsion. Alternatively, the stoppers 852 a, 852 b may be one-wayretractable, hinged, flexible, spring-loaded, or the like.

Apparatus 900 (FIG. 13) may also include a plurality of stoppers 952 a,952 b in the movement paths of the respective surfaces 10 a, 10 b. Thelocation of each of the stoppers 952 a, 952 b may be proportional to thestrength of the static field 16 experienced by the two surfaces 10 a, 10b. For example, the lowest stopper 952 a may correspond to a fieldstrength of 20 kV, the next stopper 952 a may correspond to 30 kV, andso on. In the example of FIG. 13, the stoppers 952 a, 952 b are shown inphantom when bending to allow passage of the surfaces 10 a, 10 b duringrepulsion.

While the indication of repulsion of the two surfaces 10 a, 10 b ispreferably directly observed, other indication techniques are available.For example, in FIG. 14, apparatus 1000 includes an electric circuit1054 electrically coupled to a battery 1055 and an indicator 1056. Theindicator 1056 is preferably a light. The stoppers 1052 a, 1052 b may becontact pads that are electrically coupled to the circuit 1054. Thesurfaces 10 a, 10 b are shown in the rest position in phantom. Contactbetween the stoppers 1052 a, 1052 b and the respective surfaces 10 a, 10b completes the electric circuit 1054, thereby enabling electricity toflow through from the battery 1055 to the indicator 1056. Contacts forthe electric circuit 1054 may also be separate from the stoppers 1052 a,1052 b. Alternatively, the repulsed surfaces 10 a, 10 b may break,rather than enable, the electric circuit 1054.

In certain embodiments, it may be desirable to permit motion by only oneof the surfaces 10 a, 10 b. For example, apparatus 1100 in FIG. 15 fixessurface 10 a while the other surface 10 b is free to move duringrepulsion in the presence of the static field 16. The stopper 1152 bprevents the other surface 10 b from returning to the rest position. Thefixing of one of the surfaces 10 a, 10 b may also be applicable to manyof the other embodiments described herein.

FIG. 16 illustrates an apparatus 1200 for detecting a static field 16 inaccordance with another preferred embodiment of the present invention.The apparatus 1200 includes a microelectromechanical systems (MEMS)device 1260 having two cantilevered beams 1210 a, 1210 b of conductivematerial, which is preferably a doped semiconductor material such assilicon or germanium. The cantilevered beams 1210 a, 1210 b can be verysmall, preferably having a thickness T of 100 nanometers (nm) or less.In the absence of a static field (rest position), the two cantileveredbeams 1210 a, 1210 b are adjacent and substantially parallel to eachother (FIG. 17). In the presence of a static field 16, the twocantilevered beams 1210 a, 1210 b repel each other (FIG. 16). Theapparatus 1200 further includes at least one sensor 1262 that detects anamount of repulsion of the two cantilevered beams 1210 a, 1210 b fromeach other.

The MEMS device 1260 may use conventional circuitry (not shown) fordetermining position of the cantilevered beams 1210 a, 1210 b. Thesensors 1262 are preferably capacitors, but may also be optical sensorsor the like. The sensors 1262 detect displacement of the cantileveredbeams 1210 a, 1210 b from the rest position, which is used to calculatethe repulsion of the cantilevered beams 1210 a, 1210 b from one another.A simple example of an algorithm for determining the repulsion of thecantilevered beams 1210 a, 1210 b from each other is shown by Table 1below.

TABLE 1 Measured Beam 1210a Measured Beam 1210b Repulsion ofDisplacement Displacement Beams 1210a, from Rest from Rest 1210b fromRest Position Position (Units) Position (Units) (Units) 1 1 2 2 2 4 3 36 4 4 8 5 5 10

The measured displacements of each of the respective cantilevered beams1210 a, 1210 b may be summed to attain the repulsion value. It followsfrom Table 1 that non-repulsive movement of at least one of thecantilevered beams 1210 a, 1210 b, as a result of vibrations or othermotion, results in a negative displacement value for at least one of thecantilevered beams 1210 a, 1210 b. In order to prevent false readings ofrepulsion resulting such motion, the apparatus 1200 may be programmed toignore negative displacements so that only repulsion (positivedisplacement by both cantilevered beams 1210 a, 1210 b) is reported.

The sensors 1262 may continuously determine the amount of repulsion ofthe two cantilevered beams 1210 a, 1210 b from each other, or maydetermine only whether the amount of the repulsion of the twocantilevered beams 1210 a, 1210 b is greater than a predetermineddistance.

The apparatus 1200 further includes an indicator 1264 connected to anoutput of the sensor 1262. When the sensor 1262 continuously determinesthe amount of repulsion of the cantilevered beams 1210 a, 1210 b, theindicator 1264 communicates a maximum amount of repulsion of the twocantilevered beams 1210 a, 1210 b. The amount is preferably converted toa value representing the strength of the static field 16. When thesensor 1262 determines only whether the amount of repulsion of thecantilevered beams 1210 a, 1210 b is greater than a predetermineddistance, the indicator 1264 communicates whether the amount ofrepulsion of the two cantilevered beams 1210 a, 1210 b exceeded thepredetermined distance. The indicator 1264 may be a light, alphanumericcharacters, a memory that is read out by a user, or the like.Additionally, the sensing and indication may be implemented in software.When the apparatus 1200 is used within finished equipment (e.g., a chipin a computer) (not shown), the MEMS device 1260 may be communicativelycoupled to the equipment for self-monitoring. The indicator 1264 is alsopreferably resettable to allow the apparatus 1200 to be reused.

In an alternate embodiment, apparatus 1300 shown in FIG. 18 includes twofrangible cantilevered beams 1310 a, 1310 b. At least one of the twofrangible cantilevered beams 1310 a, 1310 b fractures upon a repulsionof the two beams 1310 a, 1310 b from each other by at least apredetermined distance. Fracture may occur at any portion of therespective two beams 1310 a, 1310 b. The apparatus 1300 further includesat least one sensor 1362 to detect a fracturing of at least one of thetwo beams 1310 a, 1310 b. An indicator 1364, similar to those describedabove, may be used to indicate when fracture of the beams 1310 a, 1310 bhas occurred.

Use of the embodiments of the present invention detailed above will nowbe described. For simplicity, all embodiments hereinafter will bereferred to as static detector 2000.

FIG. 19 illustrates one of the preferred uses of the static detector2000. A printed circuit board (PCB) 2070 is shown having the staticdetector 2000 disposed thereon. The static detector 2000 is preferablyadhered or fastened to the PCB 2070. The static detector 2000 ispreferably attached to the PCB 2070 prior to manufacturing or assemblyof the PCB 2070, permitting examination of potentially damaging staticfields 16 at each stage. This is particularly useful in determining ESD“hot spots” within manufacturing equipment and permits monitoring ofcompliance with S20.20 standards.

The size of the static detector 2000 may be adjusted to suit the size ofthe PCB 2070. It is even contemplated to enable a static detector 2000to be placed on a single lead (not shown) on the PCB 2070, forindependent monitoring of the most sensitive component thereon.Placement of the static detector 2000 is not limited to PCBs 2070, butmay be placed on all kinds of ESD sensitive devices during manufacture,such as integrated circuits (ICs), wafers and chips. The staticdetectors 2000 may also be placed within the manufacturing equipment formonitoring, although placement on the PCB 2070 is preferred.

The static detector 2000 may also be placed on packaging materials, suchas a static shield bag 2072 (FIG. 20) or an IC shipping tube 2074 (FIG.21). ESD packaging materials are produced with anti-static chemicaladditives or coatings that minimize the generation or accumulation ofstatic charge within the packaging material. These chemical additivesand coatings may lose their effectiveness over time and the packagingbecomes susceptible to generating and accumulating charge. The staticdetector 2000 indicates when the static shield bag 2072, IC shippingtube 2074, or the like packaging has degraded to an undesirablecondition for ESD sensitive equipment.

As shown in FIG. 22, the static detector 2000 may also be placed in acontainer 2076 with a fluid 2077, such as de-ionized water, which isoften used in manufacturing electronics. Generation of carbon dioxide2078 or other fluid disturbances can cause static buildup, and thestatic detector 2000 indicates whether the static generated in the fluid2077 exceeds a desired level.

FIG. 23 shows a static detector 2000 positioned near one or moreionizers 2080 that place or remove charge from a material 2082. Thematerial 2082 may be, for example, a web of sheet plastic. The staticdetector 2000 provides a much smaller sensor for detecting whether theionizers 2080 are functioning properly. The static detector 2000,particularly in MEMS embodiments, could also replace the common chargeplate monitor for machines. Currently the smallest charge plate monitorsare approximately 1 inch by 1 inch. The relatively small size of thestatic detector 2000 makes it especially suited for smaller volumeswithin equipment.

For embodiments shown in FIGS. 4-15, the static detector 2000 preferablyhas the appearance to the naked eye of a dot. It may be referred to as a“static dot.” In one preferred embodiment, the static detector 2000 ispreferably generally round with a diameter of about 2 to about 3millimeters (mm).

As seen in the drawings, the static detector 2000 may include a numberof “active” and “passive” embodiments, that is, embodiments wherein thestatic detector 2000 requires or does not require power. Passiveembodiments include the embodiments shown in FIGS. 4-7, 10-13, and 15,and active embodiments include the embodiments shown in FIGS. 8-9, 14,and 16-18, although any of the embodiments shown may be modified to beactive or passive.

Passive embodiments have the advantage that no power is required, whichreduces cost and complexity of the static detector 2000. One advantageof the active embodiments is the ability to provide a wider range ofeasily identifiable indicators, such as lights. Power for activeembodiments may be supplied, for example, by an internal battery (e.g.FIG. 14), solar cells, connection to an external power supply, radiofrequency signals (similar to radio frequency identification (RFID)tags), or the like.

From the foregoing, it can be seen that embodiments of the presentinvention comprise an apparatus for detecting a static field. It will beappreciated by those skilled in the art that changes could be made tothe embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. An apparatus for detecting a static field comprising: (a) amicroelectromechanical systems (MEMS) device having two cantileveredbeams of conductive material that are adjacent and substantiallyparallel to each other, wherein the two beams repel each other in thepresence of a static field; and (b) at least one sensor that detects arespective amount of displacement of the two cantilevered beams from arest position and determines an amount of repulsion of the twocantilevered beams from each other.
 2. The apparatus of claim 1, whereinthe sensor continuously determines the amount of repulsion of the twocantilevered beams from each other.
 3. The apparatus of claim 2, furthercomprising an indicator connected to an output of the sensor thatcommunicates a maximum amount of repulsion of the two cantilevered beamsto a user.
 4. The apparatus of claim 1, wherein the sensor determineswhether the amount of repulsion of the two cantilevered beams is greaterthan a predetermined distance.
 5. The apparatus of claim 4, furthercomprising an indicator coupled to the output of the sensor thatcommunicates whether the amount of repulsion of the two cantileveredbeams exceeded the predetermined distance.
 6. The apparatus of claim 1,wherein the conductive material is a doped semiconductor material. 7.The apparatus of claim 6, wherein the semiconductor material is silicon.8. The apparatus of claim 1, wherein the at least one sensor is acapacitor.
 9. The apparatus of claim 1, wherein the at least one sensoris an optical sensor.
 10. The apparatus of claim 1, wherein theindicator is a light.
 11. The apparatus of claim 1, wherein theindicator is a memory that is read out by a user.
 12. The apparatus ofclaim 1, wherein the indicator is resettable.
 13. An apparatus fordetecting a static field comprising: a microelectromechanical systems(MEMS) device having two frangible cantilevered beams of conductivematerial that are adjacent and substantially parallel to each other,wherein the two frangible cantilevered beams repel each other in thepresence of a static field, and at least one of the two frangiblecantilevered beams fractures upon a repulsion of the two beams from eachother by at least a predetermined distance.
 14. The apparatus of claim13, further comprising at least one sensor that detects a fracturing ofthe at least one of the two frangible cantilevered beams.